The present invention relates to a mushroom-shaped semiconductor stripe laser. More particularly, the present invention relates to a mushroom-shaped semiconductor stripe laser, particularly with transversal, monomode light distribution, including a semiconductor double heterostructure comprised of a substrate, a laser-active zone, and a cover layer, as well as a respective electrically contacting metal layer for the substrate and for the cover layer, and with the cover layer being underetched such that a mushroom-shaped structure is formed in which the laser-active zone is constricted to a stripe-shaped region.
Such a semiconductor laser is also called an MS laser ("mushroom stripe laser") and is disclosed, for example, in the publication Japanese Journal of Applied Physics, Volume 22, Nov. 1983, pages L721-L723. As shown in FIG. 1, which is a schematic illustration of the cross-section of such a known MS laser, a semiconductor substrate 1 has initially applied to it a further substrate layer 1' (buffer layer). On top of the outer major surface of layer 1' is a stripe-shaped laser-active zone 2, which has a first width b1 of approximately 1.5 micron, a height of approximately 0.1 micron and a length (perpendicularly to the plane of the drawing) of, for example, 150 microns. The laser-active zone 2 is covered over its entire length by a cover layer 3 which has a height of approximately 1.5 micron and a second width b2 of approximately 15 microns. Laser-active zone 2 as well as cover layer 3 therefore form a mushroom-shaped semiconductor structure which can be produced by an etching technique customarily employed in the semiconductor art (underetching of cover layer 3). This mushroom-shaped semiconductor structure is embedded in an oxide layer 4. This embedding in an oxide layer may cause cavities 5 to be formed in the oxide layer 4 below the cover layer 3. In the region of oxide layer 4 on the outer surface of the cover layer 3, a contact window 6 is provided so that it is possible to electrically contact cover layer 3 by way of a metal layer 7. A further such metal layer 7' is also provided on the underside or opposite major surface of substrate 1. The described arrangement is a laser diode with lateral wave guidance known as an index guided laser.
The described arrangement has the drawback that the ratio of the second width b2 to the first width b1 is very large (approximately 10). This produces, particularly for industrial mass production, an uneconomical proportion of unusable semiconductor lasers. For example, the mechanical stresses produced between the oxide layer 4 and the cover layer 3 are so great that they bring about undesirable separation of the cover layer 3 from the laser-active zone 2. Moreover, during the above-mentioned underetching of the cover layer 3, undesirable fluctuations occur in the first width b1. This makes it impossible, in particular, to always guarantee that monomode light distribution is assured in the finished semiconductor laser.